These roughing end mill equipped with replaceable inserts have been proposed, for example, in Patent documents 1 and 2. In these roughing end mills, a plurality of twisted grooves are formed in an outer circumference of a circular column-shaped tool body, and square plate-shaped inserts are fitted inside these twisted grooves with a slight gap between each insert. The inserts are positioned substantially equidistantly in the twisted grooves such that the inserts of each twisted groove cover the gaps between the inserts in the other twisted grooves. Furthermore, in the conventional technology, a removable insert roughing end mill has been described in which the inserts which are fitted at the tip of the distal end of a portion of the twisted groves are formed having elongated cutting edges, and are made to overlap the cutting edges of the inserts at the tip of the distal end of the other twisted grooves. In addition, these inserts are made to overlap the distal ends of the cutting edges of the next insert in the other twisted groove. However, in the roughing end mills described in Patent documents 1 and 2, the inserts themselves are simply square plate-shaped objects having rectilinear cutting edges. Accordingly, the widths of the fragmented chips also match the length of the cutting edges and the size of the gaps between the inserts in the aforementioned twisted grooves. Because of this, it is not possible to sufficiently fragment the chips and reduce resistance, or to soften the bite impact of the cutting edges.
Therefore, in Patent document 3 the inventors of the present invention proposed inserts in which raised portions and recessed portions are formed alternatingly at substantially equal intervals so as to intersect in a cutting edge such that the cutting edge is formed in a waveform shape which undulates up and down when seen in side view and plan view, and a roughing end mill in which these inserts are mounted in mounting seats which are provided equidistantly a predetermined distance apart in one chip pocket (i.e., a chip removal groove), and in mounting seats which are provided in another chip pocket so as to be positioned between the first mounting seats in the axial direction, so that an elongated edge form is formed on the outer circumference of the end mill by the cutting edges of these inserts. Accordingly, according to this type of roughing end mill, when a cutting edge bites into a work piece, the entire length of that cutting edge does not all bite at the same time, and the work piece is bitten into gradually by the respective raised portions of the waveform. In addition, because the chips are cut into smaller fragments than the length of the cutting edges, it is possible to achieve both a sufficient impact softening and resistance reduction, and a greater improvement in the chip processability.    PATENT DOCUMENT 1: Japanese Patent Application, First Publication No. H08-1426    PATENT DOCUMENT 2: Japanese Patent Application, First Publication No. H08-1427    PATENT DOCUMENT 3: Japanese Patent Application, First Publication No. 2006-239830